Possible involvement of prolactin in endocrine-resistant metastatic prostate cancer

The hormone resistance of prostate cancer has been proved to depend at least in part on enhanced neuroendocrine activity and the resultant increase in blood concentrations of chromogranin A. Other experimental observations have suggested the involvement of prolactin (PRL), which appears to be a potential growth factor for prostate cancer. Abnormally high levels of PRL have been detected in metastatic prostate cancer, but the clinical significance of this finding has still to be clarified. In an attempt to explain the prognostic significance of serum PRL levels in prostate cancer, in this preliminary study we have analyzed the PRL levels in a group of metastatic prostate cancer patients with hormone-dependent or hormone-resistant cancer. The study included 50 patients with metastatic prostate cancer, 15 of whom had hormone-resistant tumors. The serum levels of PRL were measured by the RIA method. Abnormally high concentrations of PRL were found in 11/50 (22%) patients. Moreover, the percent of patients with cancer-related hyperprolactinemia was significantly higher in the hormone-resistant group than in the hormone-dependent group (8/15 vs 3/35, p < 0.01). This study confirms the possible existence of a hyperprolactinemic state in metastatic prostate cancer, as previously reported by other authors. Moreover, it appears to demonstrate that the occurrence of hyperprolactinemia is more frequent in hormone-resistant neoplasms, suggesting the possible involvement of PRL in hormone independence. Further studies concomitantly evaluating PRL and chromogranin A blood concentrations will be necessary to establish whether the hyperprolactinemia precedes and promotes the onset of hormone resistance in prostate cancer, or whether it is simply a consequence of the hormone independence.